1. Field of the Invention
This invention relates to a blue colored soda-lime-silica glass having a low luminous transmittance that makes it desirable for use as a privacy glazing in vehicles, such as the side and rear windows in vans or sun roofs for automotive vehicles. As used herein, the term xe2x80x9cblue coloredxe2x80x9d is meant to include glasses that have a dominant wavelength of 480 to 489 nanometers (nm) and may also be characterized as blue-green or blue-gray in color. In addition, the glass should exhibit lower infrared and ultraviolet radiation transmittance when compared to typical blue glasses used in automotive applications and be compatible with float glass manufacturing methods.
2. Technical Considerations and Prior Art
Various dark tinted, infrared and ultraviolet radiation absorbing glass compositions are known in the art. The primary colorant in typical dark tinted automotive privacy glasses is iron, which is usually present in both the Fe2O3 and FeO forms. Some glasses use cobalt, selenium and, optionally, nickel in combination with iron to achieve a desired color and infrared and ultraviolet radiation, for example, as disclosed in U.S. Pat. No. 4,873,206 to Jones; U.S. Pat. No. 5,278,108 to Cheng, et al.; U.S. Pat. No. 5,308,805 to Baker, et al.; U.S. Pat. No. 5,393,593 to Gulotta, et al.; U.S. Pat. Nos. 5,545,596 and 5,582,455 to Casariego, et al.; and European Patent Application No. 0 705 800. Others also include chromium with this combination of colorants as disclosed in U.S. Pat. No. 4,104,076 to Pons; U.S. Pat. No. 4,339,541 to Dela Ruye; U.S. Pat. No. 5,023,210 to Krumwiede, et al.; and U.S. Pat. No. 5,352,640 to Combes, et al.; European Patent Application No. 0 536 049; French Patent No. 2,331,527 and Canadian Patent No. 2,148,954. Patents such as U.S. Pat. Nos. 5,521,128 and 5,346,867 to Jones, et al. and U.S. Pat. No. 5,411,922 to Jones further includes manganese and/or titanium. Still, other glasses may include additional materials, such as disclosed in WO 96/00194, which teaches the inclusion of fluorine, zirconium, zinc, cerium, titanium and copper in the glass composition and requires that the sum of the alkaline earth oxides be less than 10 weight percent of the glass.
One particular blue composition that provides superior spectral performance is disclosed in U.S. Pat. No. 4,792,536 to Pecoraro, et al. Commercial products which incorporate this patent are sold by PPG Industries, Inc. under the trademarks SOLEXTRA(copyright) and AZURLITE(copyright). This glass has a dominant wavelength ranging from about 486 to 489 nm and excitation purity ranges from about 8 to 14 percent. It would be advantageous to be able to produce a dark tinted blue colored glass to complement this blue colored glass using conventional glass melting processing techniques.
The present invention provides a blue colored, infrared and ultraviolet absorbing glass composition having a luminous transmittance of up to 60 percent. The glass uses a standard soda-lime-silica glass base composition and additionally iron and cobalt, and optionally selenium and/or titanium, as infrared and ultraviolet radiation absorbing materials and colorants. The glass of the present invention has a color characterized by a dominant wavelength in the range of 480 to 489 nanometers and an excitation purity of at least 8 percent at a thickness of 0.160 inches (4.06 millimeters).
In one embodiment of the invention, the glass composition of a blue colored, infrared and ultraviolet radiation absorbing soda-lime-silica glass article includes a solar radiation absorbing and colorant portion consisting essentially of 0.9 to 2.0 percent by weight total iron, 0.15 to 0.65 percent by weight FeO, 90 to 250 PPM CoO, and optionally up to 12 PPM Se and up to 0.9 wt % TiO2, and preferably 1 to 1.4 percent by weight total iron, 0.20 to 0.50 percent by weight FeO, 100 to 150 PPM CoO, up to 8 PPM Se, and up to 0.5 wt % TiO2.